The efficiency of a propeller blade may be improved by decreasing the aerodynamic thickness of the profile of the propeller blade. However, reducing the thickness of a propeller blade also reduces the structural integrity of the blade. Propeller blades may need a high damage tolerance capacity in order to prevent foreign object damage (FOD) from bird impact, for example.
Propeller blades may include a structural spar to increase the structural strength of the blade. The thickness of the spar therefore limits the reduction in thickness of the propeller blade.